1. Field of the Invention
The present invention relates to terminators used for SCSI (small computer system interface) expansion buses for personal computers (PCs), and particularly, to a terminator with an indicator for indicating SCSI operating modes.
2. Description of the Related Art
SCSI buses were standardized by ANSI (the American National Standards Institute) in 1985 as connection buses between PCs and peripheral devices such as hard disks, CD-ROMs, optical disks, and MOs.
The SCSI buses first employed 50-pin connectors to transfer data, using 8 bits in parallel, at 5 megabytes per second. The SCSI buses included a single-ended SCSI bus and a high-voltage differential SCSI bus.
To improve the transfer rate, SCSI-2 was standardized in 1991. SCSI-2 includes FAST-SCSI that employs 50-pin connectors to transfer data, using 8 bits in parallel, at 10 megabytes per second and WIDE-SCSI that employs 50 -pin and 68-pin connectors to transfer data, using 16 bits in parallel, at 20 megabytes per second.
To further improve the transfer rate, SCSI-3was standardized in 1995. SCSI-3 includes ULTRA-SCSI that employs 50-pin connectors to transfer data, using 8 bits in parallel at 20 megabytes per second and ULTRA-WIDE-SCSI that employs 68-pin connectors to transfer data, using 16 bits in parallel, at 40 megabytes per second.
ULTRA-WIDE-SCSI was updated to ULTRA-2-SCSI that uses a low-voltage differential bus for transmitting data at 80 megabytes per second.
FIG. 1 is a connection diagram showing an ULTRA-2-SCSI bus system. An ULTRA-2-SCSI bus 10 connects SCSI devices 11, 12, and 13 to one another in a daisy chain.
The first SCSI device 11 is a SCSI board incorporated in a PC 1. The second and third SCSI devices 12 and 13 are, for example, hard disks.
The ends of the SCSI bus 10 are terminated by a first terminator 101 installed on the SCSI board 11 and a second terminator 102.
SCSI devices are classified into single-ended devices, high-voltage differential devices, and low-voltage differential devices. The ULTRA-2-SCSI bus 10 of FIG. 1 is fundamentally for the low-voltage differential devices and is capable of connecting not only the low-voltage differential devices but also the single-ended devices or the high-voltage differential devices.
Although the ULTRA-2-SCSI bus is capable of transferring data at 80 megabytes per second, the transfer rate is deteriorated to 20 megabytes per second between a PC and a single-ended or high-voltage differential device, if such a device is connected to the bus. In this case, a transfer rate between the PC and a low-voltage differential device connected to the bus is deteriorated to the transfer rate of 20 megabytes per second.
Then, the user will complain that the ULTRA-2-SCSI bus does not provide the specified transfer rate and make a claim to the manufacturer or dealer.
An object of the present invention is to provide a terminator with an indicator for indicating a ULTRA-2-SCSI bus operating mode, i.e., one of the single-ended, high-voltage differential, and low-voltage differential modes.
In order to accomplish the object, a first aspect of the present invention provides a terminator having a connector to be connected to a ULTRA-2-SCSI bus, a terminating unit that receives power from the ULTRA-2 -SCSI bus through the connector and connects data lines of the ULTRA-2-SCSI bus to terminating resistors, a mode detector that receives power from the ULTRA-2-SCSI bus through the connector and detects an operating mode of the ULTRA-2-SCSI bus among a single-ended mode, a high-voltage differential mode, and a low-voltage differential mode according to a voltage in a differential voltage detecting line of the ULTRA-2-SCSI bus, and a mode indicator that receives power from the ULTRA-2-SCSI bus and emits light in response to the detected operating mode.
The terminator of the first aspect is installed at an end of a ULTRA-2-SCSI bus and indicates an operating mode of the bus.
A second aspect of the present invention provides the terminator of the first aspect with an activity indicator for indicating whether or not the ULTRA-2-SCSI bus is receiving power from a ULTRA-2-SCSI device.
The second aspect indicates whether or not power is being supplied to the ULTRA-2-SCSI bus.
A third aspect of the present invention forms the mode indicator with light emitting diode (LED) drivers controlled by the mode detector and LEDs for emitting light under the control of the LED drivers.
The third aspect controls the LED drivers according to the output of the mode detector and the LEDs according to the outputs of the LED drivers.
A fourth aspect of the present invention installs the terminator in a casing. The casing accommodates the terminating unit, mode detector, and LED drivers. The connector is attached to a side face of the casing, and the LEDs and activeness indicator are attached to a front face of the casing.
The fourth aspect enables the terminator to be applied to a ULTRA-2-SCSI bus of a desktop PC.
A fifth aspect of the present invention installs the terminating unit, mode detector, and LED drivers on a circuit board. The connector is attached to a rear end of the circuit board, and the LEDs and activity indicator are attached to a front face of the circuit board.
The fifth aspect enables the terminator to be applied to a ULTRA-2-SCSI bus of a tower-type PC.